Pneumatic tire

ABSTRACT

A pneumatic tire, wherein at least one peripheral main groove ( 2 ) is provided in a tread center area and inclined main grooves ( 3 ) inclined diagonal-outward in a direction reverse to the specified rotating direction of the tire and reverse inclined main grooves ( 4 ) inclined diagonal-outward in a direction reverse to the inclination direction of the inclined main grooves are disposed on both sides of the peripheral main groove alternately in the circumferential direction of the tire, the inner ends of the inclined main grooves ( 3 ) are connected midway to the reverse inclined main grooves ( 4 ) in the area of 10 to 20% of a contact width from a tire center and the outer ends thereof are extended to shoulders, and the inner ends of the reverse inclined main grooves ( 4 ) are connected to the peripheral main groove ( 2 ) and the outer ends thereof are connected midway to the inclined main grooves ( 3 ).

TECHNICAL FIELD

[0001] The present invention relates to a pneumatic tire and, morespecifically, to a pneumatic tire in which wet braking performance anddriving stability are improved without reducing hydroplaning resistance.

BACKGROUND ART

[0002] To improve the drainage of a pneumatic tire, a tread pattern hasbeen conventionally proposed in which a rotating direction of the tireis specified in one direction (arrow R). As shown in FIG. 2, in thetread pattern, peripheral main grooves 2 are provided in the center areaof a tread surface 1, and numerous inclined main grooves 3, inclineddiagonal-outward in a direction reverse to the specified rotatingdirection R of the tire, are provided from the peripheral main grooves 2to shoulder areas at a predetermined pitch in a circumferentialdirection of the tire.

[0003] However, in this tread pattern, the shape of blocks B eachsectioned by two adjacent inclined main grooves 3 and one peripheralmain groove 2 is extremely narrowed at treading end portions Q.Accordingly, flexural rigidity is reduced in a width direction of thetire. As a result, there has been a problem that the driving stabilityis reduced on a dry road. As a measure for preventing this reduction inthe driving stability, the blocks are enlarged. Nevertheless, the grooveareas of the inclined main grooves are reduced by the amount of theenlargement, thereby causing reduction in the hydroplaning resistance.

[0004] Moreover, upon braking on a wet road, water flows from theinclined main grooves toward the peripheral main grooves. Hence, therehas been a problem that the braking performance is reduced. As a measurefor this reduction, the inclination directions of the inclined maingrooves are reversed. However, water in the inclined main grooves flowsinto the peripheral main grooves upon advancing, and the drainageperformance is reduced. This causes a problem that the hydroplaningresistance is reduced.

DISCLOSURE OF THE INVENTION

[0005] An object of the present invention is to provide a pneumatic tirein which the wet braking performance and the driving stability areimproved without reducing the hydroplaning resistance.

[0006] The pneumatic tire of the present invention achieving theforegoing object is characterized in that at least one peripheral maingroove is provided in a tread center area and inclined main groovesinclined diagonal-outward in a direction reverse to the specifiedrotating direction of the tire and reverse inclined main groovesinclined diagonal-outward in a direction reverse to the inclinationdirection of the inclined main grooves are disposed on both sides of theperipheral main groove alternately in the circumferential direction ofthe tire, the inner ends of the inclined main grooves are connectedmidway to the reverse inclined main grooves in the area of 10 to 20% ofa contact width from a tire center and the outer ends thereof areextended to shoulders, and the inner ends of the reverse inclined maingrooves are connected to the peripheral main groove and the outer endsthereof are connected midway to the inclined main grooves.

[0007] As described above, the inclined main grooves and the reverseinclined main grooves are disposed on both sides of the at least oneperipheral main groove, which is provided in the tread center area,alternately in the circumferential direction of the tire. Moreover,these three types of main grooves have specific connectionrelationships. Accordingly, it is possible to widen treading endportions of blocks, which are sectioned by the peripheral main grooves,the inclined main grooves and the reverse inclined main grooves in thetread center area. Thus, the flexural rigidity of the blocks in a widthdirection of the tire is improved, and the driving stability can beimproved.

[0008] Furthermore, when the brakes are applied to the tire on a wetroad, the reverse inclined main grooves acts on water intending to flowfrom the inclined main grooves toward the tread center so as to pushback the water outward in a width direction of the tread. Consequently,the braking performance is improved. In addition, while advancing, thereverse inclined main grooves split the flow of the water flowing inthese reverse inclined main grooves into the inclined main grooves andthe peripheral main groove, thereby contributing improvement in thehydroplaning resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a development view showing an example of a tread surfaceof a pneumatic tire of the present invention.

[0010]FIG. 2 is a development view showing an example of a tread surfaceof a conventional pneumatic tire.

BEST MODES FOR CARRYING OUT THE INVENTION

[0011]FIG. 1 is a development view of a tread surface of a pneumatictire of the present invention.

[0012] In the pneumatic tire, a direction of an arrow R is specified asa rotating direction of the tire. In the center area of a tread surface1, two peripheral main grooves 2, 2 are formed to extend linearly in acircumferential direction of the tire. A rib 5 is formed between theperipheral main grooves 2, 2. Numerous inclined main grooves 3 andreverse inclined main grooves 4 are alternately provided in both outersides of the two peripheral main grooves 2, 2 at a predetermined pitchin the circumferential direction of the tire.

[0013] The inner end of each inclined main groove 3 is connected midwayto the reverse inclined main groove 4 in the tread center area. Theinclined main groove 3 is inclined in a direction reverse to thespecified rotating direction R of the tire and extended to a shoulder.Moreover, the inclined main groove 3 extends further than a shoulder endportion to the outside. By contrast, each reverse inclined main groove 4is inclined in a direction reverse to the inclined main groove 3 withrespect to the circumferential direction of the tire. The inner end ofthe reverse inclined main groove 4 is connected to the peripheral maingroove 2, and the reverse inclined main groove 4 is extended toward theoutside of the tread. At the same time, the inner end of the inclinedmain groove 3 is connected midway to the reverse inclined main groove 4,and the reverse inclined main groove 4 is connected midway to anotherinclined main groove 3 which is adjacent to the inclined main groove 3.

[0014] In the foregoing tread pattern, the inner ends of the inclinedmain grooves 3 are disposed in positions apart from a tire center CL bya distance D of 10 to 20% of a contact width W. Herein, the position ofthe inner end of each inclined main groove 3 is determined by the centerposition of the groove width thereof. In addition, the contact width Wof the tread surface 1 is defined by a length in a width direction ofthe tire based on a contact shape measured when the tire contacts a flatroad in a state where the tire is filled and applied with a standard airand load defined by JATMA.

[0015] As described above, in the pneumatic tire of the presentinvention, the inclined main grooves 3 and the reverse inclined maingroves 4, which are mutually inclined in reverse directions with respectto the circumferential direction of the tire, are alternately disposedin the circumferential direction of the tire, and the groove endsthereof are disposed to connect midway to the grooves of each other.Thus, in blocks BL each sectioned and formed by two adjacent reverseinclined main grooves 4, one peripheral main groove 2 and one inclinedmain groove 3, an angle between the inclined main groove 3 and thereverse inclined main groove 4 formed at a treading end portion P oneach block BL can be made relatively large. Thus, the flexural rigiditywith respect to a width direction of the treading end P is increased,thereby improving the driving stability in corner running.

[0016] Moreover, upon braking on a wet road, the reverse inclined maingrooves 4 discharge part of water outward in the width direction of thetire. This prevents the concentration of water on the tread center side,thereby improving the wet braking performance.

[0017] Furthermore, in advance driving, the foregoing reverse inclinedmain grooves 4 split and send part of water flowing toward theperipheral main grooves 2, to the inclined main grooves 3. Thus, thedrainage is not prevented, and the hydroplaning resistance is notreduced.

[0018] As previously mentioned, in the present invention, the inner endsof the inclined main grooves 3 are disposed in the area of 10 to 20% ofthe contact width W of the tire from the tire center CL. When the innerends of the inclined main grooves 3 are positioned farther inside than10% of the contact width W, the blocks BL positioned in the tread centerarea are reduced. Accordingly, the flexural rigidity is reduced, and thedriving stability is reduced. On the other hand, when the inner ends ofthe inclined main grooves 3 are positioned farther outside than 20% ofthe contact width W, the length of the inclined main grooves 3 isshortened. Accordingly, the drainage performance is reduced.

[0019] In the present invention, two peripheral main grooves 2 arepreferably provided on the left and right, interposing the rib 5therebetween. The drainage in the circumferential direction is furtherimproved, and the rib 5 can improve the driving stability. Theperipheral main grooves 2 are preferably straight as in the exampleshown in the drawing. However, the peripheral main grooves 2 may bezigzagged to a certain extent if the grooves 2 are in a see-throughstate in the circumferential direction of the tire.

[0020] Moreover, in the inclined main grooves 3, it is preferable to setthe inclination angle of the inner portions from the inner ends at leastto not less than 50% of the entire length to 10° to 40°, and theinclination angle of the remaining outer portions extending to theshoulder portions to 70° to 110°, with respect to the circumferentialdirection of the tire. If the inclination angle of the inner portions ofthe inclined main grooves 3 is smaller than 10°, peripheral componentsof water flowing in the grooves are large. Hence, it is difficult todischarge the water outward in the width direction of the tire. On theother hand, if the inclination angle of the inner portions is largerthan 40°, the components in the circumferential direction of the tirebecome small. Thus, it becomes difficult for the water to move insidethe inclined main grooves 3, and thereby it becomes difficult todischarge the water outward in the width direction of the tire. Inaddition, by setting the inclination angle of the outer portions of theinclined main grooves 3 to approximately 90°, the water can beefficiently discharged outward in the width direction of the tire.

[0021] The inclination angle of the reverse inclined main grooves 4 withrespect to the circumferential direction of the tire is preferably setto 10° to 40°. If the inclination angle is smaller than 10°, theperipheral components of the water in terms of moving speed are large.Accordingly, it is difficult to discharge water outward in the widthdirection of the tire upon braking on a wet road. In addition, theflexural rigidity of the blocks, which are sectioned by the peripheralmain grooves 2, the inclined main grooves 3 and the reverse inclinedmain grooves 4, in the width direction of the tire is reduced.Accordingly, the driving stability is reduced. If the inclination angleis larger than 40°, the components in the circumferential direction ofthe tire become small. Accordingly, it becomes difficult to dischargethe water outward in the width direction of the tire upon braking on awet road surface, thereby reducing the braking performance.

[0022] Furthermore, it is preferable to provide at least one auxiliarygroove 7 approximately parallel to the inclined main grooves 3 in eachblock 6 sectioned by the inclined main grooves 3 and the reverseinclined main groove 4 from the tread center area to the tread shoulderarea. The auxiliary groove 7 is a one-side open groove in which only theshoulder end is opened, and formed shallower than the inclined maingrooves 3. In addition, in order to make the drainage better, the openside is wider than the inner side. By providing the auxiliary grooves 7,it is possible to perform drainage more effectively.

[0023] As described above, according to the present invention, thetreading end portions of the blocks sectioned by the peripheral maingrooves, the inclined main grooves and the reverse inclined main groovesare widened. Thus, the flexural rigidity in the width direction of thetire is improved, thereby improving the driving stability. Upon brakingon a wet road, the reverse inclined main grooves push back the waterintending to flow from the inclined main grooves to the center areaoutward in the width direction of the tire. Thus, the wet brakingperformance can be improved. Moreover, the reverse inclined main groovessplit the flow of the water into the inclined main grooves and theperipheral main grooves in advancing. Therefore, the hydroplaningresistance is not reduced substantially.

EXAMPLES

[0024] Two types of tires were prepared, having the same tire size of225/50R16 92V and different tread patterns. The pneumatic tire (Example)has the tread pattern in FIG. 1, in which only the auxiliary grooves areomitted. The pneumatic tire (Comparison Example) has the tread patternin FIG. 2. Both tires have the same groove width, groove depth andalignment pitch of the peripheral main grooves, inclined main groovesand reverse inclined main grooves.

[0025] The foregoing two types of pneumatic tires were fit to respectivetest vehicles. The hydroplaning resistance, the braking performance on awet road surface (wet braking performance) and the driving stability ona dry road surface were measured by the undermentioned measurementmethods. The results are listed in Table 1.

[0026] [Hydroplaning Resistance]

[0027] The speeds were measured when the first hydroplaning occurredwhile driving on a wet road with a water film of 10 mm and increasingthe driving speed gradually. The evaluations are indicated by indices,where the measured value of the tire of Comparison Example was set to100. Larger index values indicate better hydroplaning resistance.

[0028] [Wet Braking Performance]

[0029] The distances were measured from the point where the brakes weresuddenly applied to the point where the vehicle fully stopped whenentering the wet road with a water film of 10 mm at a speed of 100 km/h.The evaluations were performed with the reciprocals of the measuredvalues and indicated by indices, where the reciprocal of the measuredvalue of the tire of Comparison Example was set to 100. Larger indexvalues indicate better wet braking performance.

[0030] [Driving Stability]

[0031] Three test drivers evaluated, using a 5-point grading system, thefeeling of the steering performance when changing lanes while drivingstraight on a highway at a speed of 120 km/h. The evaluation points ofthe three test drivers were added to produce average values, which areindicated by indices, where the average evaluation point of the tire ofComparison Example was set to 100. Larger index values indicate betterdriving stability. TABLE 1 Example Comparison Example Hydroplaning  98100 Resistance (Index) Wet Braking 105 100 Performance (Index) DrivingStability 110 100 (Index)

[0032] From Table 1, the tire of Example (present invention) improvesthe wet braking performance and the driving stability while maintainingthe hydroplaning resistance substantially at the same level as the tireof Comparison Example (conventional example).

INDUSTRIAL APPLICABILITY

[0033] The present invention can be utilized in a pneumatic tire for anyof vehicles for passengers and for heavy-loads such as trucks and buses.Especially, the present invention is effective for pneumatic radialtires. Furthermore, the present invention is suitable for a pneumaticradial tire for passenger vehicles.

What is claimed is:
 1. A pneumatic tire, wherein at least one peripheralmain groove is provided in a tread center area and inclined main groovesinclined diagonal-outward in a direction reverse to a specified rotatingdirection of the tire and reverse inclined main grooves inclineddiagonal-outward in a direction reverse to an inclination direction ofthe inclined main grooves are disposed on both sides of the peripheralmain groove alternately in a circumferential direction of the tire,inner ends of the inclined main grooves are connected midway to thereverse inclined main grooves in an area of 10 to 20% of a contact widthfrom a tire center and outer ends thereof are extended to shoulders, andinner ends of the reverse inclined main grooves are connected to theperipheral main groove and outer ends thereof are connected midway tothe inclined main grooves.
 2. The pneumatic tire according to claim 1,wherein two of the peripheral main grooves are provided, interposing arib therebetween.
 3. The pneumatic tire according to any one of claims 1and 2, wherein angles of the inclined main grooves with respect to thecircumferential direction of the tire are set to 10° to 40° for innerportions from the inner ends thereof to at least 50% of a lengththereof, and to 70° to 110° for outer sides from the inner portions. 4.The pneumatic tire according to claim 3, wherein an angle of the reverseinclined main grooves with respect to the circumferential direction ofthe tire is set to 10° to 40°.
 5. The pneumatic tire according to anyone of claims 1 and 2, wherein at least one auxiliary groovesubstantially parallel to the inclined main grooves is provided in ablock sectioned by two of the adjacent inclined main grooves and one ofthe reverse inclined main grooves.
 6. The pneumatic tire according toclaim 3, wherein at least one auxiliary groove substantially parallel tothe inclined main grooves is provided in a block sectioned by two of theadjacent inclined main grooves and one of the reverse inclined maingrooves.
 7. The pneumatic tire according to claim 4, wherein at leastone auxiliary groove substantially parallel to the inclined main groovesis provided for a block sectioned by two of the adjacent inclined maingrooves and one of the reverse inclined main grooves.